The development of higher speed microprocessor chips and the miniaturization of the power conversion circuitry (usually switch-mode supplies) used to power these chips have lead to an increase in the demand for small footprint, low ESR capacitors. These capacitors need to minimize voltage output fluctuations at the switching frequency and harmonics of the power supply. They also are used to provide local power to the microprocessor chip to maintain power supply voltages at acceptable limits as the current demands of the processor shift.
Power supplies operating at switching frequencies of 100 kHz and above are one such type of device. It is important that the capacitor exhibit low impedance and equivalent series resistance (ESR) at these frequencies as well as low equivalent series inductance (ESL). The capacitors used in such power supplies should have large low frequency charge storage so the power supply can experience momentary variations in input power without disturbing the output.
Previously, electronics manufacturers have used combinations of metal oxide and ceramic capacitors that are mounted in parallel and connected by a variety of connection circuits to provide charge storage and acceptable high frequency impedance/ESR performance. Unfortunately, the available space for mounting such systems of chips is diminishing as manufacturers design ever smaller and more efficient systems. Manufacturers must also incur costs per mounted connection to assemble such circuits, and variations in the interconnecting circuitry cause differences in the resulting ESL between board manufacturers.
It would be advantageous to have a capacitor element with low impedance and ESR at high frequencies that could be mounted in a minimum amount of space on a circuit board.
It would also be beneficial to have a means for reducing variations in ESL for parallel mounted metal oxide and ceramic capacitors.